Manipulation of plants to alter and/or improve phenotypic characteristics (such as productivity or quality) requires the expression of heterologous genes in plant tissues. Such genetic manipulation relies on the availability of a means to drive and to control gene expression as required. For example, genetic manipulation relies on the availability and use of suitable promoters which are effective in plants and which regulate gene expression so as to give the desired effect(s) in the transgenic plant.
The root-preferential or root-specific promoters are useful for alteration of the function of root tissue, modification of growth rate, improvement of resistance to root preferred pathogens, pests, herbicides or adverse weather conditions, for detoxification of soil as well as for broadening the range of soils or environments in which said plant may grow. Root abundant or root specific gene expression would provide a mechanism according to which morphology and metabolism may be altered to improve the yield and to produce useful proteins in greater amounts. In particular, root specific promoters may be useful for expressing defense-related genes, including those conferring insectical resistance and stress tolerance, e.g. salt, cold or drought tolerance, and genes for altering nutrient uptake.
A limited number of examples of root preferred and root-specific promoters have been described. These include the RB7 promoter from Nicotiana tabacum (U.S. Pat. Nos. 5,459,252 and 5,750,386) the ARSKI promoter from Arabidopsis thaliana (Hwang and Goodman (1995) Plant J. 8:37:43), the MR7 promoter from Zea mays (U.S. Pat. No. 5,837,848), the ZRP2 promoter of Zea mays (U.S. Pat. No. 5,633,363), and the MTL promoter from Zea mays (U.S. Pat. Nos. 5,466,785 and 6,018,099). Many of these examples disclose promoters with expression patterns confined to a limited number of root tissues. Other fail to provide the root specificity needed for expression of selected genes. It is advantageous to have the choice of a variety of different promoters so that the most suitable promoter may be selected for a particular gene, construct, cell, tissue, plant or environment. Moreover, the increasing interest in cotransforming plants with multiple plant transcription units (PTU) and the potential problems associated with using common regulatory sequences for these purposes merit having a variety of promoter sequences available.
There is, therefore, a great need in the art for isolation and characterization of new root-specific or root-preferential transcription regulating sequences which offer a broad spectrum of breadth, expression level and specificity of root cell-type expression, that can be used for expression of selected transgenes in economically important plants. It is thus an objective of the present invention to provide new and alternative expression cassettes for root-preferential or root specific expression of transgenes in plants. The objective is solved by the present invention.